A. Field of the Invention
This invention relates to ultraviolet radiation curable compositions suitable for use as optical coatings for use in photographic films.
Manufacturers of photographic films have been attempting to perfect three-dimensional-effect color films for some time. One approach currently under investigation is to deposit a clear, lenticulated optical coating onto conventional photographic print material. The optical coating is responsible for the three dimensional effect and is usually composed of a cross-linked, ultraviolet-radiation-cured acrylic polymer supported by a clear plastic base such as cellulose triacetate, polypropylene, or polyester. The optical coating is typically 8-11 mils (0.008-0.011 inch) thick. Lenticulated optical coatings are described in J. Nims et al, "Three Dimensional Pictures And Method Of Composing Them," U.S. Pat. No. 3,852,787 (Dec. 3, 1974).
An optical coating should possess several characteristics; foremost among them is optical clarity. The optical coating must not be susceptible to yellowing or other discoloration prior to, during, and after exposure and developing of the color print material underlying the optical coating.
In addition to optical clarity, the optical coating must be sufficiently flexible so as not to crack when the film is bent in half.
The physical characteristics of the optical coating are highly dependent upon the choice of acrylate-terminated oligomers employed in the manufacture of the optical coating. In addition to providing a cured acrylic optical coating which satisfies the requirements discussed above, the uncured optical coating composition should possess a rapid cure rate, thereby allowing processing speeds of at least 15 feet per minute and preferably 30-60 feet per minute.
Typically, acrylate-terminated oligomers which possess polyester or polyether backbones have been employed in the manufacture of optical coatings. Polyester-based acrylic coatings display poor hydrolytic stability. Conventional water-based photographic developers can easily penetrate polyester-based acrylic optical coatings, thereby causing severe yellowing of the optical coating. Polyether-based acrylic coatings suffer from poor oxidative stability, and are also permeable to photographic developers.
In copending patent application Ser. No. 419,676, filed Sept. 20, 1982, now abandoned, we disclose optical coating compositions which employ polyurethane-based acrylate-terminated oligomers.
B. Description of the Prior Art
H. Hisamatsu et al, "Photopolymerizable Isocyanate-Containing Prepolymers," U.S. Pat. No. 3,891,523 (June 24, 1975) discloses UV curable, acrylate-terminated polyurethane prepolymers which have a free isocyanate content of from 0.3 to 15 percent based on the total weight of the prepolymer and a cure initiator. The excess isocyanate groups are stated to impart superior adhesion to a substrate.
N. Miyata et al, "Photopolymerizable Vinylurethane Monomer," U.S. Pat. No. 3,907,865 (Sept. 23, 1975) discloses acrylate-terminated polyurethane oligomers which are highly UV curable and which, upon curing, form a non-yellowing acrylic film. The reference requires the use of xylylene diisocyanate in the preparation of its acrylate-terminated polyurethane oligomer.
D. Lorenz et al, "Radiation Curable Coating Composition Comprising An Acryl Urethane Oligomer And An Ultra-Violet Absorber," U.S. Pat. No. 4,129,667 (Dec. 12, 1978) discloses an acrylate-terminated, polyether or polyester-based polyurethane oligomer which is employed in combination with an acrylic ultraviolet radiation absorber.
D. Lorenz et al, "Radiation Curable Coating Composition Comprising An Acryl Urethane Oligomer And An Ultra-Violet Absorber," U.S. Pat. No. 4,135,007 (Jan. 17, 1979) discloses a radiation curable coating composition comprising an acrylate-terminated, polyether or polyester-based polyurethane oligomer and a benzylidene acid ester.
H. Suzuki et al, "Thermosetting Resins," U.S. Pat. No. 4,020,125 (Apr. 26, 1977) discloses an acrylate-terminated hydrogenated polybutadiene polymer which may be cured by exposure to electron beam radiation. The thermoset resin so produced has utility in electrical components.